As is well known, a communication system may utilize multiple communication channels to communicate signals between transmitters and receivers of the system. For example, multiple channels may be used to separate different transmitted data signals from one another, or to provide an increased data rate.
A problem that can arise in multiple channel communication systems relates to crosstalk between the various channels, also referred to as inter-channel crosstalk. For example, in a typical digital subscriber line (DSL) system, each of the channels may comprise orthogonal frequency division multiplexed (OFDM) tones transmitted over a physical communication link such as twisted-pair copper wire. A transmission on one subscriber line may be detected on other subscriber lines, leading to interference that can degrade the throughput performance of the system. More generally, a given “victim” channel may experience crosstalk from multiple “disturber” channels, again leading to undesirable interference.
Techniques for compensating for inter-channel crosstalk in a communication system are described in U.S. patent application Ser. No. 60/922,703, filed Apr. 9, 2007 and entitled “Determining a Channel Matrix by Measuring Interference,” which is commonly assigned herewith and incorporated by reference herein. In one approach disclosed in the above-cited patent application, off-diagonal elements of a channel matrix are estimated using signal-to-interference-plus-noise ratios (SINRs) measured by a receiver and communicated from the receiver back to the transmitter. The resulting channel matrix may be used to compensate for the inter-channel crosstalk.
Despite the considerable advantages provided by the exemplary techniques described in the above-cited patent application, a need remains for further improvements, particularly in terms of estimating channel crosstalk in DSL systems and other communication systems that may include unsynchronized channels.